feat(blog): add copyable highlighted code blocks

src/lib/markdown-headings.ts

@@ -0,0 +1,52 @@
+export type MarkdownHeading = {
+  id: string;
+  level: 1 | 2 | 3;
+  text: string;
+};
+
+function plainHeadingText(value: string) {
+  return value
+    .replace(/`([^`]+)`/g, "$1")
+    .replace(/\*\*([^*]+)\*\*/g, "$1")
+    .replace(/\*([^*]+)\*/g, "$1")
+    .replace(/\[([^\]]+)\]\([^)]+\)/g, "$1")
+    .replace(/<[^>]*>/g, " ")
+    .replace(/\s+/g, " ")
+    .trim();
+}
+
+function headingIdBase(text: string) {
+  const normalized = text
+    .normalize("NFKC")
+    .toLowerCase()
+    .replace(/[^\p{L}\p{N}\s_-]/gu, "")
+    .trim()
+    .replace(/\s+/g, "-")
+    .slice(0, 80);
+
+  return normalized || "section";
+}
+
+export function extractMarkdownHeadings(content?: string): MarkdownHeading[] {
+  const counters = new Map<string, number>();
+
+  return (content || "")
+    .split(/\r?\n/)
+    .map((line) => {
+      const match = /^(#{1,3})\s+(.+?)\s*#*$/.exec(line.trim());
+      if (!match) return null;
+
+      const level = match[1].length as 1 | 2 | 3;
+      const text = plainHeadingText(match[2]);
+      const base = headingIdBase(text);
+      const nextCount = (counters.get(base) || 0) + 1;
+      counters.set(base, nextCount);
+
+      return {
+        id: nextCount === 1 ? base : `${base}-${nextCount}`,
+        level,
+        text,
+      };
+    })
+    .filter(Boolean) as MarkdownHeading[];
+}